1. Field of the Invention
This invention relates to a process or method for refining ferrophosphorus for use in the production of phosphorus containing iron, steel and alloys thereof.
Ferrophosphorus is usually obtained as a by-product from well known thermal processes for the production of elemental phosphorus. The ferrophosphorus by-product usually contains 20 to 30% phosphorus, 50 to 75% iron, and may contain varying small amounts of vanadium, chromium, titanium, manganese and nickel, depending upon the composition of the phosphate rock used in the process. Additionally, ferrophosphorus may contain elemental silicon in values in excess of 1 percent.
Through the use of ferrophosphorus in iron and steel making processes, desirable amounts of phosphorus can be incorporated in the resulting alloys. In many of these alloys, however, the presence of elemental silicon in excess of 1 percent in the alloying agent produces an adverse effect upon the properties of the alloys because of the solubility of silicon in the molten metal. It has therefore been desirable to select ferrophosphorus having a low silicon content, 1 percent being acceptable while 0.05 percent is preferred. This invention discloses a method for refining ferrophosphorus containing in excess of 1 percent elemental silicon to enable its use as a phosphorizing substance in the iron and steel making process where the elimination of the deleterious effects of silicon is required.
2. Description of the Prior Art
Processing ferrophosphorus to reduce the elemental silicon content to levels acceptable for use in iron and steel making is not new in the art. A method used to indirectly reduce the elemental silicon content has been the selection of raw materials used to produce elemental phosphorus. By proper selection of the raw materials, elemental silicon levels in the ferrophosphorus by-product can be controlled. This method generally increases costs because of the selectivity required for the raw materials. Alternatively, ferrophosphorus can be subjected to processes to remove the undesirable elemental silicon or to convert it to silica which is insoluble in the molten iron and steel.
In U.S. Pat. No. 3,744,999, there is disclosed a composite composition comprising high silicon content ferrophosphorus admixed with a solid oxidizing agent and integrally composited. This composite composition is then added to the molten iron or steel causing the silicon to be oxidized to silica. It is essential that the composition possess certain "critical characteristics" including: (1) an oxidizing agent which is solid at ambient temperature and a thermally stable liquid at the temperature of molten iron; and (2) thorough mixing and compositing so that upon addition to a molten metal bath, the oxidizing agent will remain in integral contact with the ferrophosphorus for a length of time sufficient to effect oxidation of the silicon contained therein. The invention of this disclosure is distinguishable in that it requires neither of these "critical characteristics" as will be explained hereafter.